                                 \begin{tabular}{l*{2}{c}} \hline \hline \\                                                 & \multicolumn{7}{c}{\shortstack{World ranking}} \\                                                 \cmidrule(l){2-8}                                                   & \multicolumn{1}{c}{\shortstack{1--20}}                                                  & \multicolumn{1}{c}{\shortstack{21--50}}                                                 & \multicolumn{1}{c}{\shortstack{51--100}}                                                 & \multicolumn{1}{c}{\shortstack{101--250}}                                                 & \multicolumn{1}{c}{\shortstack{251--500}}                                                  & \multicolumn{1}{c}{\shortstack{501--1000}}                                                  & \multicolumn{1}{c}{\shortstack{1001--2000}}                                                 & \multicolumn{1}{c}{\shortstack{Unranked}} \\                         
\hline \\
World rank: 1--20&    0.338\sym{***}&    0.285\sym{***}\\
                &  (0.024)         &  (0.017)         \\
[1em]
World rank: 21--50&    0.206\sym{***}&    0.175\sym{***}\\
                &  (0.015)         &  (0.013)         \\
[1em]
World rank: 51--100&    0.211\sym{***}&    0.157\sym{***}\\
                &  (0.013)         &  (0.011)         \\
[1em]
World rank: 101--250&    0.142\sym{***}&    0.105\sym{***}\\
                &  (0.011)         &  (0.010)         \\
[1em]
World rank: 251--500&    0.119\sym{***}&    0.100\sym{***}\\
                &  (0.010)         &  (0.009)         \\
[1em]
World rank: 501--1000&    0.079\sym{***}&    0.137\sym{***}\\
                &  (0.010)         &  (0.009)         \\
[1em]
World rank: 1001--2000&    0.073\sym{***}&    0.107\sym{***}\\
                &  (0.008)         &  (0.008)         \\
[1em]
World rank: Unranked&                  &    0.051\sym{***}\\
                &                  &  (0.004)         \\
\\ \hline \noalign{\smallskip} 
N: Rank 1--20   &       19         &       18         \\
N: Rank 21--50  &       22         &       22         \\
N: Rank 51--100 &       38         &       34         \\
N: Rank 101--250&      103         &       79         \\
N: Rank 251--500&      154         &      100         \\
N: Rank 501--1000&      221         &      133         \\
N: Rank 1001--2000&      317         &      184         \\
N: Rank Unranked&     1999         &      774         \\
N: Total        &     2873         &     1345         \\
Adjusted R$^2$  &     0.20         &     0.48         \\
                                 \hline \hline \noalign{\smallskip}                                 \end{tabular}                         
